1. Field of the Invention
The present invention relates to a method for dimensional stabilization treatment of wood and wood composite. In particular, it relates to a method for treatment of wood or wood composite which comprises supplying high pressure steam to wood or wood composite under reduced pressure to cause the high pressure steam to penetrate into interior of the wood or wood composite and which is thereby capable of improving dimensional stability of wood or wood composite.
2. Description of the Prior Art
Wood swells and contracts by absorption and exhalation of moisture. The same is true of a plain lumber, a plain thin wood board (thickness: about 0.2 mm to about 10 mm), a particle board, an MDF (medium density fiberboard), an OSB (oriented strand board) and the like. When wood or wood composite is used as a constructional material or furniture material, it is undesirable that the wood or wood composite should swell or contract under the influence of surroundings. Accordingly, wood or wood composite is desired to have dimensional stability less affectable by surroundings.
As measures to deal therewith, a method has been proposed which comprises placing wood or wood composite held between upper and lower press platens in an autoclave, and treating the wood or wood composite with high pressure steam for several minutes to dimensionally stabilize the wood or wood composite. However, this method has disadvantages in that the equipment is undesirably large, and that the high pressure steam doses not penetrate well into interior (center or core portion) of the wood or wood composite, and accordingly, the wood or wood composite is likely to be differently treated between its center portion and peripheral portion.
The inventors of the present application have made extensive experiments and researches to solve the disadvantages, and as a result, they have proposed a method which comprises placing wood or wood composite to be treated between upper and lower hot platens of a press whose hot platens are of a type used in conventional wood treatment, placing an elastic sealing member made of an elastic silicone around the wood or wood composite and a predetermined thickness regulating jig made of a stainless steal or the like around the elastic sealing member to hermetically contain the wood or wood composite, and supplying high pressure steam thereto through steam supplying openings formed in the upper and lower platens to effect dimensional stabilization of the wood or wood composite (Japanese Unexamined Patent Publication No.238616/1994, European Unexamined Patent Publication No.611638).
The treating method disclosed in the publications has advantage in that a press having usual hot platens used in pressing of wood or production of a composite may be used, and accordingly, simple diemnsional stabilization treatment of wood or wood composite is realized. Further, the method for dimensional stabilization treatment of wood or wood composite by means of high pressure steam is capable of applying dimensional stabilization treatment to wood or wood composite without using any chemical agent such as phenol or hormalin, and thus, the method advantageously leaves no chemical agent after the treatment.
While repeatedly practically carrying out the dimensional stabilization of wood or wood composite in accordance with the above treating method, the present inventors have experientially found that in some cases, high pressure steam is not uniformly distributed throughout the wood or wood composite dependently upon, for example, specific gravity, thickness, size, surface condition of the wood or wood composite, and consequently, an intended dimensional stability cannot be attained. In particular, in a natural woodboard prepared by simply cutting a natural wood such as a plain lumber or thin woodboard, pits which are interconnectively present between vessels and tracheids and contribute to movement of moisture are closed. Accordingly, it is difficult even, for example, by preliminary hot-air circulation heating to discharge moisture contained in the interior of such a natural woodboard to the outside, leading to a long drying time. On the other hand, if high pressure steam is supplied, it does not penetrate well into the interior of the woodboard. In consequence, it is difficult to attain desired dimensional stability.
Further, a large amount of energy is required to obtain such high pressure steam having a high temperature. In view of this, it is desired that amount of the high pressure steam be minimized to save a treating cost.
Moreover, if wood or wood composite at room temperature in normal condition, which generally has a water content of at least about 8% to about 10% and a temperature of about 15.degree. C. to 25.degree. C., is placed in a sealed space defined between hot platens or the like without having been subjected to any preliminary treatment, energy of high pressure steam (saturated steam or superheated steam) generated at high cost is used to heat the wood or wood composite to a raised temperature capable of vaporizing moisture contained in the wood or wood composite and of converting the moisture into high pressure steam. This is consumptive in terms of treating time and energy. In addition, if wood or wood composite is a natural woodboard prepared by simply cutting a natural wood such as a plain lumber or thin woodboard, internal moisture is not readily discharged and high pressure steam does not penetrate well, as described above. This leads to a prolonged treating time.